Gun drill guides are well known in the art. They are used to help prevent the tendency of the drill shaft to whip, bow and vibrate when the drill is operated at relatively high rpms. However, such whipping, bowing and vibration cannot fully be overcome with a gun drill having only one cutting edge because the drill shaft is off balance and not on the center of gravity. Thus, the gun drill shaft includes a V-shaped angle which changes the center of gravity and the drill shaft whips off center at the middle, between the guide supports for the shaft. Gun drill guides further function as a seal between the drill and the edges of an opening of a chip box through which the drill shaft extends and prevents the passage of lubricant and chips from the chip box around the drill.
Gun drill guides are disclosed, for example, in U.S. Pat. Nos. 3,361,014 and 5,181,812, which disclosures are incorporated herein by reference. Gun drill guides are also sold by The Whip Guide Company under the trademark GIZMO®.
A prior art gun drill guide is shown in FIG. 7 and consists of a cylindrical body member C of resilient polymer having a non-round central opening extending therethrough (not shown) and which includes a radially extending flange F at one end which engages a bearing assembly end face and a second radially extending flange F′ at the opposite end and of lesser diameter than the flange F. Flange F′ is of uniform thickness in the x direction. It engages an opposite bearing end face. Flanges F and F′ are intended to hold the guide in place. The guide is inserted into a bearing, the bearing having a radius at each end face opening of the bearing. The guide must be pushed into the bearing and cylindrical body C fits snugly against the inner annular wall of the bearing. Thus, flange F′ is pushed through the bearing opening, requiring a degree of force and deformation of flange F′. Accordingly, flange F′ must remain somewhat pliable and can only be of a certain diameter and thickness. In use, as the bearing turns at high RPMs, e.g. 2000-10,000, the guide heats up. The heat causes the polymer of the guide to become more pliable and the guide tends to pop out of the bearing as flange F′ is not of sufficient diameter or structure to hold it in place. This is necessarily detrimental and affects the efficiency and quality of the gun drilling operation and increases the expense of operation. When a drill guide pops out, the drill and the whip guide supports have to be disassembled to remove and replace the guide with a new one. This takes about 10 to 15 minutes.
Other prior art guides include a cylindrical body portion, a radially extending flange at one end thereof and an annular groove at the opposite end thereof which receives a snap ring to hold the guide in place. This type of prior art guide eliminates the force required to insert the guide, but requires the use of the snap ring. In practice, such guides also have a tendency to pop out of the bearing when the drill is operated at high rpms.
The tendency of a gun drill to whip, bow and vibrate is particularly a problem with smaller drill sizes such as one-quarter inch or smaller. This movement of the gun drill adversely affects the quality and efficiency of the gun drilling operation. If the gun drill whipping is controlled, the gun drill can be operated at higher rpms providing a higher chip rate, thereby allowing the drilling of gun barrels in 25% to 200% faster time. This provides a higher quality product and at a reduced cost. When using prior art guides at such higher RPMs, this generates even more bearing heat which results in the guide getting even hotter, thereby softening the guide and causing the guide to pop out of the bearing even more frequently.
The prior art gun drill assemblies utilize a deflector to deflect the metal chips and the chip lubricant generated during the drilling operation. The chip deflection prevents these materials from damaging the drill guide and the bearing in the chip box. The prior art chip deflectors consist of an annular plastic support having a metal disc on each side. The chip deflector includes a central opening generally sized to fit the drill shaft. The chip deflector fits on the drill shaft and floats on the shaft, generally toward the back of the chip box because of the lubricant pressure pushing it back. These chip deflectors have a tendency to get stuck on the drill shaft because chips get stuck behind it or the plastic seal gets damaged, all of which requires manual removal and down time of the machine. Also, when the chip deflector gets stuck on the shaft, the chip deflector moves forward with the drill shaft toward the workpiece causing the chips to clog the hole in the workpiece. If the drill is not stopped within seconds, estimated at about 3 to 15 seconds depending on drill feed ratio, to manually unstick the chip deflector, the drill shaft will bend between the whip guide supports, break the shaft and also break the drill tip off of the shaft.
As previously stated, the prior art chip deflectors get stuck and move forward on the shaft causing chips to build up in the drilled hole. Such build-up affects the cooling lubricant pressure since higher pressure is required to push the chips out of the drill hole. This is particularly problematic when drilling deep holes and requires higher lubricant pressure.
U.S. Pat. No. 5,181,812 discloses another type of chip deflector. This chip deflector incorporates a metal shield in the drill guide flange when molding the drill guide. The metal shield is said to prevent the drill guide from eroding when the guide flange is exposed in the chip box to the impingement of metal chips and/or the cutting lubricant. In practice, this is not used extensively or at all due to the extra step, difficulty and expense in molding this type of drill guide.
Accordingly, while the prior art gun drill guides and chip deflectors have been useful up to a point, improvement is necessary to overcome the above disadvantages and to provide more efficiency to the gun drilling operation.